1. Technical Field
The present invention relates to a substrate processing apparatus and, more particularly, to a semiconductor processing apparatus equipped with a heat exchanger having an excellent temperature control performance.
2. Related Art
A substrate, an opposite electrode, a target and the like in plasma processing apparatuses such as a sputtering apparatus or an etching apparatus used for manufacturing a semiconductor device or a liquid crystal display panel are heated by the plasma or the ion bombardment. Therefore, in order to prevent a temperature rise and perform stable processing continuously, a cooling mechanism is installed, which maintains them at a predetermined temperature.
For example, in a cooling mechanism of sputtering target, as shown in FIG. 6, a depression which a cooling water pass through is formed in the rear face of a backing plate 102 on which a target 101 is fixed, and the backing plate is fixed on a target holder 103 so as to cover the depression (JP6-172988A). Fins 104 are provided in the depression to reinforce the plate and to form a cooling water channel 106. The target 101 is cooled with the cooling water which is introduced into channel 106 from a cooling water inlet port 105 and is discharged from an outlet 107. Thus, with the reinforcement fin 104, the backing plate can be made thinner, which therefore improves the efficiency to cool the target
Similarly, the coolant channels are also provided inside a substrate holder and an opposite electrode of etching apparatus. The coolant flowing through the channel maintains the substrate and the gas emitting plate at a predetermined temperature to attain stable processing.
However, when semiconductor devices such as LSI are requested to have the higher density and the higher degree of integration to a design rule of 0.13 μm, the cooling capacity of cooling mechanism became insufficient and caused to increase the temperature distribution over the substrate, and made it difficult to maintain the uniformity of etching rate. Therefore, it was necessary to increase the cooling capacity by lowering the temperature of coolant, or increasing the flow rate. However, this method increases the loads of a coolant pump and, for example, a chiller of thermostatic bath, resulting in cost rise of apparatus.
Furthermore, since the shape of, e.g., the contact holes to be formed is sharply changed with the temperature of substrate, the temperature rise must be as small as possible during the processing for a single substrate from the etching processing beginning to the end. Accordingly, the heat transfer of cooling mechanism should be improved so as to be able to adopt the coolant at a higher temperature.
Then, the present inventors have investigated and examined the relation between the internal structure of a heat exchanger and the cooling capacity, and found that the cooling efficiency is improved by providing fins inside the cooling channels and further improved without the conductance drop of flow by providing the fins nealy parallel with the flow direction.
The spacing of fins is preferably made as small as possible in order to further increase the cooling efficiency. However, when the spacing becomes small to a certain degree, a cutting tool cannot enter into the groove between the fins. That is, the fin structure wherein the spacing is less than the width of cutting tool has not been able to be fabricated and in other words the higher fin density has been actually impossible. Then, the present inventors attempted to fix the fins with, e.g., blazing and found that the heat transfer was sometimes decreased in the blazed positions. The fins were not aligned precisely, which caused the non-uniform flow. Thus, the temperature distribution became non-uniform over the whole substrate surface to deteriorate the etching characteristics and its uniformity.